Removing the polycarbonate F.B:
You should have no problem removing a molded polycarbonate f.b. completely by prying it up by starting with a flat chisel at the nut forcing it down toward the face of the uke. If its not already loose, we generally stand the uke upright on a hard surface, hammer the chisel between the nut and the neck parallel with the f.b. Once it breaks loose, work the chisel down the neck to separate the f.b. Stop before reaching the bottom where the f.b. is attached to the sound board. At this point you need to be very careful not to peel off the top. We generally keep thumb pressure between the f.b. and sound hole and twist the f.b. to the side to break loose the bond without disturbing the top. The f.b. material is pretty tough and the old hot glue usually sticks to the wood.
With the original hot glue still in place, you can glue the new poly f.b. directly to the old glue. Any good cyanoacrylate super glue will work or universal two part epoxy. Apply it sparingly to minimize squeeze out. Clamp evenly or wrap with tape being careful to remove any glue from the finish with mineral spirits.
Replacing with hardwood:
You can also purchase a hardwood replacement f.b. however it requires removing the old hot glue from the neck. This is best done by clamping the neck to a flat surface and carefully using a hammer and chisel to remove the old glue completely.
Once the old glue is removed and the wood f.b. can be glued in place with any good quality PVA wood glue. The f.b. must be positioned properly relative to the bridge for proper intonation. For a concert Fluke, the distance from the highest point on the bridge, and the center of the zero fret is 15.06" (15 1/16”), a soprano Flea measures 14.06" (14 1/16”) and tenor is 17.06” (17 1/16”). Clamp evenly or wrap tightly with tape or elastic such as a strip of bicycle inner tube. Two hours of clamping should be sufficient and then clean up with damp cloth to remove excess dried glue.